Studies aimed at the elucidation of the immune mechanisms involved in the host's response to allogeneic tissue placed in the anterior chamber of the rat's eye are planned. It has become quite clear that alloantigens presented to the host in this body compartment have profound immunoregulatory effects on the total immune response. Since it is well established that the host's immune system recognizes the alloimplanted tissues placed in the anterior chamber of the eye long before it brings about complete rejection of that tissue, studies are proposed which will characterize the nature of the factor in the implant bearing rat's serum which is capable of blocking lymphokine production. Further studies will be performed which will determine under what circumstances that blocking factor is produced and lost in the serum. In addition, studies are proposed to determine how suppressor cells are involved in the "privileged nature" of the anterior chamber of the eye.